The interaction of geological and anthropic processes shaping the urban growth of Ferrara and the evolution of the surrounding plain.

The town of Ferrara is placed at the junction of the alluvial plain of the Po River, the innermost portion of the Po River delta plain, and the alluvial plain fed by the Reno River and other Apennines-derived streams. The depositional evolution of the fluvial system largely affected the urban shape, but human intervention in turn modified the river dynamics, to eventually subjugate it into the present-day artificial state. Ferrara is the only city of the Emilia region not sharing Roman or a pre-Roman origin; the future urban region was nevertheless well populated during ancient times. During Roman times major artificial intervention was performed on the natural river framework, through long canal digging and river embankment. After the fall of the Roman Empire, a major restructuring of the river drainage system took place, leading to the development of two new distributary channels. Ferrara nucleated during the early Middle Ages (7th century), near the divergence point of these channels, as a Byzantine fortified structure, built on a crevasse splay, part of the northern levee body of the main Po channel of the time. The southern side of the fortified village, was about 240 m long, its area 35,000 squared metres. The proto-urban structure then grew in a linear way, on the levee crest, since the elevated site offered protection against flooding waters and provided comparatively firm and well drained ground. During the first half of the 11th century, the urbanised area on the northern levee broadly stretched over a distance of about 2300 m, with a width of often less than 100 m Also the southern levee of the Po di Ferrara was progressively overbuilt, during the Middle Ages. At the beginning of the 12th century, the present-day Po channel, flowing at the north of the town, was generated, through an river reorganisation phase traditionally known as Rotta di Ficarolo. During the same century, the Romanesque cathedral was founded, at the distal edge of the sedimentary levee complex. During the following centuries, the early growth way of the urban tissue through individual building cell implantation gave way to discrete episodes of town growth and district planning. Land reclamation works made the expansion of the urban area toward interfluvial argillaceous depressions possible. At the ending of the 15th century, this northward expansion culminated into a large renaissance expansion (Addizione Erculea). During the following century, the water flow in the southern Po delta channels was suddenly terminated by an ill-fated attempt to artificially force the Reno River to reach the sea through the former Po di Primaro channel. The very low topographic gradients and the elevated sediment load transported by this Apennines-derived river rapidly silted up the ancient Po di Ferrara channel, just at the west of the town. Large marsh therefore developed in the areas surrounding the town. After a long period of stagnation, the urban growth restarted only during the 20th century, in ways utterly unaware of the geological and environmental constrains and thus exposed to significant level of environment hazards, such river floods and earthquakes.